The purposes of this study are: (1) To determine the dose-response relationship among single intravenous doses of RS-25259 over the dose range 0.3-30 ug/kg. The primary endpoint will be the proportion of patients with a complete antiemetic response (no vomiting or retching) for 24 hours after highly emetogenic chemotherapy, in chemotherapy-naive cancer patients. The efficacy of each dose will be compared with the efficacy of the lowest dose. (2) To assess the safety of single intravenous doses of RS-25259 administered through the range of doses tested in this patient population. (3) To assess the pharmacokinetics of single intravenous doses of RS-25259 through the range of doses tested in this patient population.